A disclaimer: creating this poll was a bit of a catch-22, as I could not include all PHP frameworks (would have been a very long list) and had to make a selection based on popularity; of course that meant a guess by using Twitter and google results, but the ultimate popularity of the framework, at least in the audience of Web Builder Zone, would only be established by a poll.

I have added more options after the initial comments in the first day of the poll. I hope the poll won't be skewed by this addition. I feel I have to mention Yii: I've got several comments, but late in time and adding it would have not represented the audience very well, as other frameworks got already votes for the previous three days.

I thank you for the participation and the suggestions: we had more than one thousand votes, and this means we gathered responses from a statistically valid sample of the PHP community.

The results

After having closed the poll, the results say Zend Framework wins with the 35% of votes, followed by Symfony and CodeIgniter.

Why these three frameworks have a great market share in the PHP community? Surely their time to market was optimal, but that is true also for CakePHP and others.

I think one important factor is that they're backed by a company, which is a great guarantee for receiving technical support and avoiding obsolescence:

Of course, large contributions on the code are coming from the PHP community and its passionate users. I can say this from the inside for Zend Framework, as some of my patches were integrated in the past.

However a company-based contribution is really helpful for an open source project. When you make money by using and extending the framework, and can influence its development direction, and you have the incentive to work on it more and more. This results in an higher quality of the product: we all see the effect that commercial Linux distributions had on the operating system.

CakePHP for example, is powered by a foundation, which accepts donations. Kohana is also donation-powered, and developed only by volunteers. Probably many of these volunteers work in their day jobs with the framework, but it's not the same as having a company that puts you to work on the framework as your day job like Zend did with Matthew Weier O'Phinney.

Conclusion

Good news for open source: you can make money out of it, since there are businesses which pursue development of Zend Framework, Symfony and CodeIgniter. Development of the framework it's not their primary occupation (they sell services, like most of us), but this business model is one of the "motives" why software is open sourced.

I think that Zend Framework will suffer a bit in the future to the advantage of Symfony 2, due to its 2.x version being late to the market than the former, for which preview releases are already available. The second iteration of PHP frameworks is coming, with innovations (for the PHP world) like integration with a Data Mapper such as Doctrine 2, an architecture influenced by PHP 5.3 and its namespaces and closures, and the abandonment of too magic features to reduce the complexity of understanding an application.